Convection and diffusion limited aeration during biooxidation of shallow ore heaps

Biooxidation of an ore heap containing only a few percent of sulfide minerals requires insertion of a very large amount of oxygen either by natural air convection, forced air ventilation or gaseous diffusion. While shallow heaps, those with large areas relative to their height, are of great interest for many gold and copper heaped ore processing operations, natural convection is often ineffective for oxidizing them because of inadequate lateral flow to the heap's interior. However, even in the absence of airflow, oxygen can diffuse into a shallow heap from its upper, horizontal surface in contact with air. Oxygen diffuses through the air-filled void space within the heap, driven by the oxygen concentration gradient resulting from internal oxygen depletion caused by mineral oxidation. Oxygen diffusion, coupled with the chemical reaction kinetics oxidizing the sulfide minerals, is analyzed for typical ore heap biooxidation parameters. Practical limits on bath natural convection and gaseous diffusion for effective biooxidation of the sulfide minerals in shallow ore heaps are discussed.